The present invention relates to a color-toner-use fixing unit and a color image forming apparatus both in a copying machine, a printer and a facsimile machine, and in particular, to a color-toner-use fixing unit which is capable of instant heating and is for quick start fixing, and a color image forming apparatus employing the same.
Heretofore, as a fixing unit used for a copying machine, a printer and a facsimile machine, those of a heat roller fixing system have been used widely for a low speed machine up to a high speed machine and for machines for monochromatic images and full-color images, as a stable and highly sophisticated one.
In the fixing unit of a conventional heat roller fixing system, however, when heating a transfer material and toner, there has been a problem that it is disadvantageous for energy conservation because of poor effect of energy conservation because a fixing roller with great heat capacity needs to be heated, and a long time is required for warming a fixing unit in the course of printing, resulting in a long printing time (warming-up time).
A fixing unit of a film fixing system wherein a film (heat fixing film) is used to solve the above-mentioned problem, a heat roller is changed to a heat fixing film having an ultimate thickness and low heat capacity, heat conduction efficiency is extremely improved by bringing the temperature-controlled heater (ceramic heater) into direct contact with the heat fixing film, and thereby, energy conservation and quick start which hardly requires warming-up time are achieved, and a color image forming apparatus employing the fixing unit of a film fixing system, have been proposed, and they are used recently.
Fixing methods wherein a light transmitting base body representing a variation of the heat roller is used as a fixing roller, and heat ray emitted from a halogen lamp provided inside is projected on toner to heat and fix the toner and quick start requiring no warming-up time is achieved, are disclosed in TOKKAISHO Nos. 52-106741, 52-82240, 52-102736 and 52-102741.
However, in the method disclosed by TOKKAISHO No. 52-106741 wherein heat ray or heat wave from a halogen lamp is projected through a light transmitting base body to heat and fix toner, there is a problem that it is difficult to melt and fix with heat ray due to different spectral characteristics when applying to color image forming, and it is especially difficult to melt and fix color toner images having different spectral characteristics and superposed on a transfer material and having a thick toner layer, with heat ray, although energy conservation and quick start in which a warming-up time is shortened are achieved. Color reproduction and a gloss resulting from sufficient fusion of toner are needed, and as color toner, there is used polyester resin with low molecular weight having sharp melt property, and a soft roller which forms a sufficient nipping section for fixing is generally used in the fixing unit.